One example of a refrigeration apparatus provided with conventional vapor compression type refrigerant circuits is air conditioning systems used to air-condition office buildings. This kind of air conditioning system includes chiefly a heat source unit having a compressor and a heat-source-side heat exchanger, a plurality of user units having user-side heat exchangers, and gaseous refrigerant piping and liquid refrigerant piping for connecting said units together. In view of such environmental concerns as destruction of the ozone layer, HFC (hydro-fluorocarbon) based refrigerants and HC (hydrocarbon) based refrigerants have come to be used in this kind of air conditioning system.
When air conditioning systems in existing buildings are replaced, the existing gaseous refrigerant piping and liquid refrigerant piping are sometimes used in order to reduce the cost and time required for the replacement work. In such cases, the air conditioning system installation work proceeds according to the following steps:                1) Recover refrigerant        2) Install equipment        3) Install piping and wiring (reuse existing gaseous refrigerant piping and liquid refrigerant piping)        4) Perform airtightness test        5) Pull vacuum        6) Charge system with refrigerant        7) Perform test run        
With this work procedure, the work time can be reduced chiefly by simplifying the piping and wiring work.
However, debris, oil, and other residual contaminants that remain in existing gaseous refrigerant pipes and liquid refrigerant pipes must be removed by cleaning the piping before performing a test run of the system. More particularly, if old oil for CFC (chlorofluorocarbon) or HCFC (hydro-chlorofluorocarbon) based refrigerants remains in the existing gaseous refrigerant piping and liquid refrigerant piping when existing gaseous and liquid refrigerant piping is reused for a new air conditioning system, the old refrigerant oil will not be compatible with the new oil for the HFC or HC based refrigerant and will behave as a contaminant in the refrigerant circuit, possibly clogging expansion valves and capillaries in the refrigerant circuit and damaging the compressor.
The oils used for the conventional CFC and HCFC based refrigerants are naphthene-based mineral oils and other non-polar oils. Conversely, the oils used for the newer HFC and HC based refrigerants are ester-based and ether-based mineral oils and other non-polar oils. Consequently, if oil for the CFC or HCFC based refrigerant remains in the piping, the solubility of the oil in the refrigerant will change and the proper refrigeration performance will not be obtained from the HFC or HC based refrigerant. Thus, it is also necessary to clean the piping in view of this issue of oil compatibility.
An air conditioning system that enables existing gaseous refrigerant piping and liquid refrigerant piping to be used is disclosed in Japanese Laid-Open Patent Publication No. 2001-41613. This air conditioning system is provided with a main refrigerant circuit that includes a compressor, a user-side heat exchanger, and a heat-source-side heat exchanger and an oil recovery device provided in the gas intake pipe of the compressor. After the air conditioning system is charged with the HFC based refrigerant, the compressor is run in a mode (pipe cleaning mode) that circulates the refrigerant and cleans the piping with the circulated refrigerant. The residual oil that remained in the existing gaseous refrigerant piping and liquid refrigerant piping is recovered by the oil recovery device.
The oil recovery device is provided in such a manner as to bypass a portion of the gas intake pipe. Thus, with this air conditioning system, the refrigerant circuit can be changed over so that the oil recovery device is not used during normal operation. However, after operation in pipe cleaning mode, contaminants including old refrigerant oil remain in the branched inlet and outlet pipes that lead into and out of the oil recovery device from the gas intake pipe and there is the possibility that these contaminants will be returned to the gas intake pipe and cause damage to the compressor downstream or other problems when the system is operated in a normal mode.
Furthermore, there is a gate valve installed at the outlet side of the oil recovery device for disconnecting the oil recovery device from the main refrigerant circuit. If liquid refrigerant remains in the oil recovery device when the gate valve is closed after pipe cleaning mode, overpressuring of the container might occur due to evaporation of the residual liquid refrigerant.
Also, there are times when pipe cleaning using such an oil recovery device is conducted by circulating refrigerant that is in a wet state (gas-liquid two-phases) through the refrigerant circuit. When this type of operation is conducted, liquid refrigerant collects in the oil recovery device and causes the quantity of refrigerant circulating through the refrigerant circuit to decrease, which sometimes impedes sufficient cleaning of the piping.
Thus, in some respects, conventional system configurations utilizing an oil recovery device are not sufficiently reliable when the system is run in pipe cleaning mode.